Certain vehicles, such as bulldozers, use a hydrostatic drive system. Typically, an engine-driven hydraulic pump provides a flow of pressurized hydraulic fluid to a hydraulic motor. The hydraulic motor is coupled to wheels (or tracks) of the vehicle. Thus, by driving the hydraulic motor, it is possible to maneuver the vehicle. The vehicle includes brakes, and to prevent overheating of the brakes, pressurized flow of the hydraulic fluid to the hydraulic motor should substantially cease prior to the brakes being applied.
It is known to provide a “dump valve” between the engine-driven hydraulic pump and the hydraulic motor. Opening of the dump valve causes the hydraulic pump and the hydraulic motor to vent to a tank, thereby ceasing driving input to the vehicle wheels. Once the dump valve is open, the brakes are then applied. In this way, the brakes are only required to slow the vehicle and do not act against any driving force of the hydraulic pump and the hydraulic motor.
Furthermore, certain other vehicles, such as agricultural tractors that do not typically use a hydrostatic drive system, are known to use a combined brake master cylinder and booster. Vehicles that use hydrostatic drive systems, such as the bulldozers discussed above, do not use a combined brake master cylinder and booster. Similarly, vehicles that use a combined brake master cylinder and booster do not have hydrostatic drive systems.
In combined brake master cylinder and boosters, brake pedal effort applied via a push rod is increased (or boosted), and a boosted force is applied to a master cylinder. Thus, such a device assists an operator of the vehicle when braking. Typically, the device is utilized with a mechanically driven vehicle. Thus, in order to apply the brake, the operator will typically have taken a foot off an accelerator pedal to apply it to a brake pedal, or alternatively will simultaneously depress a clutch pedal with one foot and the brake pedal with another foot. In either event, the driving input to the vehicle wheels ceases via a mechanism other than the combined brake master cylinder and booster. In other words, the combined brake master cylinder and booster plays no part in the ceasing of the driving input to the vehicle wheels.